1. Field of the Invention
The present invention relates to methods and apparatus for bleaching clothes and, more particularly, relates to techniques for "stone-washing" clothes using pumice rock impregnated with potassium permanganate.
2. Description of the Background
Stone-washing of garments has become increasingly popular in the past decade. This process generally consists of exposing the garments, such as jeans, to a combination of bleaching and an abrasive material, so that the jeans become both faded and appear to have been worn. The worn appearance desired by stone-washing may be obtained by (1) tumbling the garments with an abrasive stone, metal, or plastic material in a "dry" process, (2) tumbling the garments in a washing machine wherein the internal walls of a washing machine cylinder have been previously abraded by a volcanic rock, (3) washing the garments in water containing pumice rock, as generally described in German specification No. DE129699, or (4) agitating the garments in water and pumice sand, as disclosed in U.S. Pat. No. 4,575,887.
With respect to the first technique described above, the desired stone-washed appearance can be obtained by impregnating the pumice rock with potassium permanganate or other bleaching solutions. Pumice rock is an ideal abrasive material for achieving the desired worn appearance for the garments, and impregnated pumice rock allows the bleaching and abrasive functions to co-act with very favorable results. One of the significant problems with the pumice rock tumbling technique, however, relates to the difficulty of getting the bleaching solution to completely impregnate the pumice rock. Pumice rock is generally lighter than the potassium permanganate solution, and thus floats on the solution. Pumice rock has heretofore been placed in perforated buckets and forced down into a potassium permanganate solution, so that the solution impregnates the outer layer of pumice rock. The rock with the impregnated outer layer is then tumbled with the garments as described above in the stone-washing process. After the batch of garments has been tumbled, the garments are typically separated from the reduced diameter rock, which typically has its outer layer worn off by the abrasive tumbling action. A new outer layer of the rock is then generally reimpregnated and the rock reused in another batch process, until the rock or stones are reduced to an impractically small size, at which time the stones are discarded.
The impregnation of wood with preservatives or fire retardant liquids has long been accomplished by immersing the wood in liquid, then applying pressure to the liquid to drive the liquid into the wood, as disclosed in U.S Pat. Nos. 3,671,299 and 3,460,979. U.S. Pat. No. 4,433,031 discloses a special polymer for impregnating wood, wherein the wood is placed in a sealed chamber, a vacuum of at least twenty-six inches of mercury is drawn on the container, the wood is immersed in liquid while still under a reduced pressure, and pressure is increased to a level of about 350 psi to drive the liquid into the wood. Others have suggested the use of wave energy (U.S. Pat. No. 3,551,190) and sonic vibration (U.S. Pat. No. 3,639,152) to assist in impregnation of wood with a liquid preservative.
Metal castings intended to be subjected to pressure have long been impregnated with resins to seal porosity and prevent leakage. In many instances, the impregnation of metal castings seeks to seal the exposed surfaces of the castings rather than to impregnate the entire casting. The casting may be immersed in liquid and a vacuum then drawn on the chamber holding the castings (wet vacuum), or the vacuum may be first drawn on the chamber in which the castings are placed and liquid added (dry vacuum). In either case, the vacuum is released to achieve the effect of driving the resin into the outer skin layer of the casting. According to the disclosures of U.S. Pat. Nos. 4,311,735 and 4,384,014, pressure is subsequently applied to the chamber to assist in driving the liquid into the castings. A centrifuge for recovering excess impregnating liquid is disclosed in U.S. Pat. No. 4,196,231, and a special pressure vessel with porous support members is disclosed in U.S. Pat. No. 4,620,991.
An application roller for pressing an impregnating material into stone plates to seal the plates is disclosed in U.S. Pat. No. 4,620,989. U.S. Pat. No. 4,013,809 discloses a technique for sealing porous block, wherein the block is placed in a liquid-tight flexible bag which is then subjected to a vacuum, and a resin fed into the bag to immerse the block. A continous process for removing air from fruits and vegetables is disclosed in U.S. Pat. No. 3,052,209.
Although several porous objects, principally wood and metal castings, have long been impregnated with liquids with the assistance of vacuum, those skilled in the art of bleaching clothes and stone-washing fabrics have heretofore not recognized the applicability of technology associated with impregnating porous objects for stone-washing and, particularly, for impregnating pumice rock with a bleaching solution. Moreover, the characteristics of pumice rock and the purpose served by using pumice rock impregnated with a bleaching liquid as an integral step of a fabric bleaching process have historically been considered distinct from the characteristics of wood or castings and the techniques associated with impregnating those objects to retard decay and/or seal the object's surface.
The disadvantages of the prior art are, however, overcome by the present invention, and improved methods and apparatus are hereinafter disclosed for giving garments a worn and bleached or "stone-washed" appearance utilizing pumice rock impregnated to its core with a selected bleaching solution, such as potassium permanganate.